Organic electronics have drawn research interest in recent years because of their potential for broad commercial application, including electroluminescence devices, field effect transistors and organic photovoltaics (OPVs), etc. In all these devices, the key component is organic semiconducting material, which is usually used as one or more active thin layers. OPVs offer a practical path to achieve low-cost, renewable energy. OPVs have several advantages that their inorganic counterparts lack that allows for strong potential of lower cost implementation. The advantages of organic electronics include their ability to be solution processed into large-area thin-films, to be fabricated into lightweight and flexible devices, and the capacity to tune their properties through organic synthesis. To ultimately replace their inorganic, silicon-based counterparts, organic materials that give the highest possible power conversion efficiency (PCE) for the lowest possible cost are needed.
Among organic semiconductors, alternating conjugated polymers of an electron-donor (ED) unit and an electron-acceptor (EA) unit have attracted attention due to their special properties associated with the donor/acceptor (D/A) structure in the main chain. This D/A structure can effectively lower the band gap of conjugated polymers, especially for solar cell applications, where the polymer absorption can be fine-tuned to match the solar spectrum. Meanwhile, the energy offset between lowest unoccupied molecular orbital (LUMO) of the polymer and, for example, fullerene derivatives (widely used electron acceptors in organic solar cells) should be well controlled to be just enough to allow for charge separation in order to minimize energy loss. However, to fine tune the energy levels (highest occupied molecular orbital (HOMO), LUMO) of the conjugated polymer, while simultaneously optimizing other properties, such as solid state packing, solubility, carrier mobility still tends to be difficult.
One of the best performing classes of conjugated polymers is based on an ester functionalized thieno[3,4-b]thiophene (MTT) and alkoxy-substituted benzodithiophene (PTB1). Among these, the polymer with the highest, most regularly reported PCE is a fluorinated derivative of PTB1 (known as PTB7), synthesized from an F-MTT monomer, used in OPVs with over 9% efficiency.

Fluorinated conjugated polymers show several advantages compared with their non-fluorinated counterparts. First, they usually have lower HOMO and LUMO energy levels, which will increase open circuit voltage of photovoltaic devices and endow the polymer better resistance against oxidative degradation processes. Second, because of high electronegativity of fluorine, the resulting polymers can be used as n-type or ambipolar semiconducting materials. Third, the fluorinated compounds can form C—H . . . F interactions in some instances, which can influence the solid state supramolecular organization, phase segregation and π-π stacking of the polymeric material. These features may enhance the charge carrier mobility. Despite these beneficial properties, the number of fluorinated monomers with strong electron withdrawing ability for use in OPVs is quite limited.
Additionally, synthesis of F-MTT, for example, involves many steps (11 steps), includes difficult chemistry, and significant amounts of purification, all of which contribute to PTB7 being one of the most expensive materials for OPVs. PTB7 sees widespread academic use, but is currently impractical for industrial scale production. When compared among other polymers and small molecules commonly used in OPVs, PTB1 is one of the most expensive in number of dollars per grams and per steps. PTB7 is slightly more expensive as it requires even more reagents and steps than PTB1. There is a need in the art for improved syntheses of organic photovoltaic monomers, oligomers, and polymers as well as a wider variety of OPV monomers.